What are organisations and what they are not, why do they exist and
how do they tend to change over a period of time?

Any group of people can decide that they are an organization in the
USA and most other locations. Typically the organization changes
rapidly as old members loose interest or move away and new memembers
take over either officially or unofficially.
 If they choose, the organization can become a not for profit
corporation. Even if it does not, it is a good idea for someone to
learn the rules of not for profit, as it may avoid legal troubles.  
Neil

Hi zaibraja,

This question looks like part of an organisation theory assignment.

So your search on Google should look a little like this:

organisation + theory
OR
organization + theory 
OR
organizational + theory
OR
"organization science"

Please note that you'll get more results if you search using US
spelling (organization) as well as the English (organisation).

The Google Directory lists some good resources too:

Business > Management > Organizational Change > Publications > Articles 
http://directory.google.com/Top/Business/Management/Organizational_Change/Publications/Articles/?il=1

Business > Management > Organizational Change > Publications > Articles 
http://directory.google.com/Top/Business/Management/Management_Science/Organization_Science/?il=1

Hope that helps,

* j *

An organization is a group of people united for a common purpose. 
This requires some formal structure if business transactions will be
entered into in a legal manner.  They change as their common purpose
evolves due to changing interest among the group's members and the
environment in which it exists changes.

From this foundation you can branch into legal organization structure
or go into isses of organization change & development.